The present invention relates to a method of manufacturing halogen cycle incandescent lamps, and more particularly multifilament lamps for use in automotive applications.
It was customary to use fused silica or quartz glass for the bulb of this type of halogen cycle lamp. This required complex processing, especially as regards the achievement of hermetic glass-to-metal seals. Due to the cost involved, the use of hard glass for halogen cycle incandescent lamps became of interest, for the price of hard glass compared with the price of fused silica is lower not only for the material as such but also for its processing, last but not least because it permits lower processing temperatures. Hard glass compositions are borosilicate compositions having a mean coefficient of linear thermal expansion between 0.degree.to 300.degree. C. .times.10.sup.-7 per .degree.C. (.alpha.), ranging from 30 to 50 and having an annealing point above 500.degree. C. The previously used manufacturing sequences were found to be inapplicable to hard glass as the bulb material for halogen cycle incandescent lamps. Hard glass, moreover, permits new structural designs.
It is the object of the present invention to provide a suitable method of economic manufacture of halogen cycle incandescent lamps provided with bulbs of hard glass.